Substance system

ABSTRACT

A one-component dispersion comprising deactivated isocyanates which cross-links already at low temperatures (lower than 70° C.).

CROSS REFERENCE TO RELATED APPLICATIONS/PRIORITY CLAIM

This U.S. Patent has been granted based on a U.S. National Phase PatentApplication based on International Patent Application PCT/DE 99/00223,filed Jan. 29, 1999, upon which a claim of priority is made, and which,in turn, claims priority based on German Patent Application DE 198 20270.9, filed May 7, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a one-component dispersion.

2. Discussion of the Prior Art

Nowadays, high performance adhesive bondings are achieved according tothe state of the art with reactive adhesives. For this purpose, a seriesof different adhesive systems is known. Due to their high reactivity,polyisocyanates are used for many applications in this field.

There are, for example, isocyanate-terminated polymers which cross-linkafter the application with moisture. The disadvantage of these systemsis that curing takes a long time since cross-linking is dependent on thediffusion rate of water. Furthermore, cross-linking can remainincomplete in the case of very thick layers.

Two-component adhesives are mixed immediately before their application,which comprises an additional step for the user. Moreover, whilepreparing the two-component systems, errors may occur in proportioningor in mixing.

Further, one-component systems are known which may be formulated byblocking isocyanates with monofunctional reactants. Said blocking isthermally reversible, so that at elevated temperatures the blockingagent is separated and the released isocyanate forms a thermostable bondwith the reactive polymer groups by cross-linking.

The disadvantage of these systems is that, if said blocking agent isvolatile at application temperature, it vaporizes and may thus burdenthe environment or, if said blocking agent remains in the adhesives, itmay lead to a deterioration or degradation as to the quality of saidadhesives.

European referance 0 204 970 discloses a process for the production ofstable dispersions of fine powdered polyisocyanates in a liquid bytreating said polyisocyanates with stabilizing agents. In order toproduce storage-stable dispersions of polyisocyanates and especiallysolid polyisocyanates and in order to prevent a premature, undesiredreaction with the dispersion medium, the dispersed isocyanates aredeactivated on their surface. They then possess a so-called retardedreactivity.

European referance 0 204 970 further discloses the use as a cross-linkerfor said stable dispersions of fine powdered polyisocyanates producedaccording to the process of said document. The stabilization of thepolyisocyanates is obtained by the application of a polymeric shell. Thecompounds used to enable this polymeric shell are called stabilizingagents. The deactivated polyisocyanates, which comprise said polymershell, are called stabilized polyisocyanates. The disadvantage here isthat the burst or break-up of the polyurea capsules and thuscross-linking occurs at a temperature between 70 and 180° C.

SUMMARY AND DESCRIPTION OF THE INVENTION

Thus, the object of the present invention is to provide a one-componentdispersion cross-linking at low temperatures.

Said problem is solved by a one-component dispersion comprisingdeactivated isocyanates as a cross-linking component. Applicantssurprisingly found out that the use of encapsulated or deactivatedisocyanates, which are known per se, as cross-linking agents in aqueousdispersions leads to storage-stable systems cross-linking already attemperatures lower than 70° C.

It is assumed that the self-adhesion forces arising during the formationof the polymeric film mechanically destroy the polymeric shells of theisocyanates, thus leading to a cross-linking reaction which can be shownon the basis of the increase of film cohesion or the reduction of filmelasticity, respectively.

The one-component dispersion according to the present invention has theadvantage that it cross-links at relatively low temperatures, especiallyat room temperature, thereby avoiding the disadvantages of stable priorart one-component systems. Compared with prior art two-componentadhesives, the one-component dispersions of the present inventionprovide the advantage that they exclude the possibility of errors inapplication by the user, e.g. proportioning or mixing errors.

According to one embodiment of the present invention, the amounts ofdeactivated isocyanates in the one-component dispersions of the presentinvention are within the range of from 0.1% by weight up to 20% byweight, and especially of from 1% by weight up to 10% by weight.

The one-component dispersions of the present invention may be used in amultitude of applications, e.g. as a paint or a lacquer, as a coating,as a sealing material, as a casting material and/or as an adhesive.

When used as an adhesive, a suitable dispersion adhesive according tothe present invention may contain, for example, Dispercoll® KA 8758.According to the present invention, suitable isocyanates are, forexample, MDI or TDI, such as TDI-urethdione or TDI-urea. Theseisocyanates are deactivated according to the method known per se, andthe resulting deactivated isocyanates are then added to an appropriatepolymer such as a dispersion adhesive, while stirring. When thedeactivated isocyanate is homogeneously and smoothly incorporated, theone-component dispersion of the present invention is ready to be used.

The one-component dispersion of the present invention can advantageouslybe used, for instance, for the bonding of three dimensional furniturefronts. These types of furniture fronts are produced in such a way,nowadays, that a plastic film or foil is pressed to a contoured mediumdensity fiberboard carrier under pressure while applying heat, so thatthe film or foil takes the shape or the contours of the medium densityfiberboard surface. The friction-type bond between the two substratesrequires an adhesive which has previously been applied to the carrier.It is known that in order to realize high performance bonding with goodheat stability, two-component polyurethane dispersion systems are used,wherein the aqueous dispersion is mixed with the water-emulsiblepolyisocyanate immediately before use. Due to proportioning errors orinsufficient homogenization an optimal heat stability cannot be reached.Furthermore, the pot-life of these two-component systems is limited to afew hours only.

The above-mentioned disadvantages can advantageously be avoided by usingthe one-component dispersion adhesive of the present invention.

Examples are described in the following.

EXAMPLES Example 1

Synthesis of Deactivated Isocyanates

Example 1.1

100 ml of cyclohexane are placed into a beaker and 20 g of aTDI-urethdione (Desmodur® TT, Bayer AG) are suspended while stronglystirring. Then, a solution of 0.06 g of methylpentamethylenediamine(Dytek® A, DuPont) in 50 ml of cyclohexane is added. After a stirringtime of two hours, the resulting solution is removed from the solvent sothat a fine, white powder is obtained.

Example 1.2

The synthesis process corresponds to that of Example 1.1, however, aTDI-urea (Desmodur® LS 2116, Bayer AG) is used instead of saidTDI-urethdione.

Example 2

Production and Cross-linking of One-component Dispersion Adhesives

The deactivated isocyanates from Examples 1.1 and 1.2 are added toDispercoll® KA 8758 while stirring. Stirring should continue until theisocyanates are homogeneously and smoothly incorporated.

The cross-linking of the storage-stable one-component dispersionadhesives at room temperature is clearly shown in the followingexamples:

Comparative Example

Thermoplastic one-component dispersion: 100 g Dispercoll® KA 8758

Example 2.1

Cross-linkable one-component dispersion: 100 g Dispercoll® KA 8758 and 4g of deactivated isocyanate according to Example 1.1

Example 2.2

Cross-linkable one-component dispersion: 100 g Dispercoll® KA 8758 and 4g of deactivated isocyanate according to Example 1.2

Films having a thickness of 1000 μm are obtained using a filmdrawingbar, dried (20° C./65% relative humidity) and stored. The tensilestrength of these films is determined using a tensile testing machine.The results obtained are listed in the following table.

TABLE 1 Tensile strength of one-component dispersion adhesives whichwere cross-linked at room temperature Tensile Strength in N/mm²Comparative Days* Example Example 2.1 Example 2.2 4 7.2 10.5 13.4 7 7.313.1 14.6 14 7.1 13.8 13.3 28 6.5 11.2 15.2 *Films were stored at roomtemperature.

It can be seen from Table 1 that the tensile strength of the ComparativeExample after a 4-, 7-, 14-or 28-day storage of the films at roomtemperature, respectively, is within the range of between 6.5 and 7.3N/mm². The tensile strength of the films of Example 2.1 and Example 2.2is significantly higher than the tensile strength of the films of theComparative Example: The film of Example 2.1 showed a tensile strengthof between 10.5 and 13.8 N/mm² at the given storage time, while the filmof Example 2.2 showed a tensile strength of between 13.3 and 15.2 N/mm².

The viscosity of the produced one-component dispersion adhesives ofExample 2.1 and Example 2.2 remained constant for a storage time ofthree months at room temperature.

Thus, while there have been shown and described and pointed outfundamental novel features of the present invention as applied to apreferred embodiment thereof, it will be understood that variousomissions and substitutions and changes in the form and details of thedevices illustrated, and in their operation, may be made by thoseskilled in the art without departing from the spirit of the presentinvention. For example, it is expressly intended that all combinationsof those elements and/or method steps which perform substantially thesame function in substantially the same way to achieve the same resultsare within the scope of the invention. Substitutions of elements fromone described embodiment to another are also fully intended andcontemplated. It is also to be understood that the drawings are notnecessarily drawn to scale but that they are merely conceptual innature. It is the intention, therefore, to be limited only as indicatedby the scope of the claims appended hereto.

What is claimed is:
 1. A storage-stable, cross-linkable aqueousone-component dispersion comprising: (a) solid diisocyanates consistingessentially of solid diisocyanates which have been surface-deactivatedor encapsulated with an amine selected from the group consisting ofdi-and polyamines so as to have a retarded reactivity, saidsurface-deactivated or encapsulated diisocyanates being present in anamount within a range of 0.1% by weight to 10% by weight based on thetotal weight of the aqueous dispersion and being selected from the groupconsisting of toluene-diisocyanates (TDI), TDI-urethdione, TDI-urea and4,4′-methylene-di(phenylisocyanate) (MDI), and (b) a polyurethane baseddispersion adhesive as a polymer component, so that films produced fromthe dispersion are cross-linkable at room temperature (20° C., 65%relative humidity) without heating.
 2. The one-component dispersionaccording to claim 1, wherein said one-component dispersion has aviscosity that remains constant at room temperature for a storage timeof about three months.
 3. The one-component dispersion according toclaim 1, wherein the films obtained from said dispersion and having afilm thickness of 100 μm show a minimum tensile strength of 10.5 N/mm²after a storage for 4, 7, 14 and 28 days at room temperature.
 4. Anadhesive, comprising a storage stable, cross-linkable, aqueousone-component dispersion comprising (a) solid diisocyanates consistingessentially of solid diisocyanates which have been surface-deactivatedor encapsulated with an amine selected from the group consisting ofdi-and polyamines so as to have a retarded reactivity, saidsurface-deactivated or encapsulated diisocyanates being present in anamount within a range of 0.1% by weight to 10% by weight based on thetotal weight of the aqueous dispersion and being selected from the groupconsisting of toluene-diisocyanates (TDI), TDI-urethdione, TDI-urea and4,4′-methylene-di(phenylisocyanate) (MDI), and (b) a polyurethane baseddispersion adhesive as a polymer component, so that films produced fromthe dispersion are cross-linkable at room temperature (20° C., 65%relative humidity) without heating.
 5. A film comprising: soliddiisocyanates consisting essentially of solid diisocyanates which havebeen surface-deactivated or encapsulated with an amine selected from thegroup consisting of di-and polyamines so as to have a retardedreactivity, said surface-deactivated or encapsulated diisocyanates beingpresent in an amount within a range of 0.1% by weight to 10% by weightbased on the total weight of the aqueous dispersion and being selectedfrom the group consisting of toluene-diisocyanates (TDI),TDI-urethdione, TDI-urea and 4,4′-methylene-di(phenylisocyanate) (MDI),and (b) a polyurethane based dispersion adhesive as a polymer component,so that the film is cross-linkable at room temperature (20° C., 65%relative humidity) without heating.
 6. The film according to claim 5,wherein the film has a thickness of 1000 μm and shows a tensile strengthof at least 10.5 N/mm² after a storage for 4, 7, 14 and 28 days at roomtemperature.
 7. The storage-stable, cross-linkable aqueous one-componentdispersion of claim 1, wherein the diisocyanates are selected from thegroup consisting of toluenediisocyanates (TDI), TDI-urethdione andTDI-urea.